Until recently most of known polymerizable compounds undergo positive shrinkage in volume on polymerization. Thus, for example, ethylene, vinyl chloride, methyl methacrylate and styrene will give rise to calculated shrinkages of 66.0% 34.4%, 21.2% and 14.5%, respectively, during the addition polymerization, as reported by William J. Bailey in J. Macromol. Sci. Chem. A9(5), pp. 849-865(1975). In cationic ring-opening polymerization of hitherto known monomers such as epoxides, considerable shrinkage in volume will also take place, although the shrinkage degree in that case will often be less than that observed during the addition polymerization. By way of reference, calculated shrinkages of some epoxides which will occur on ring-opening polymerization are as follows:
ethylene oxide: 23%; propylene oxide: 17%; PA1 styrene oxide: 9%; epichlorohydrin: 12%; PA1 2,2-dimethylethylene oxide: 20%. PA1 Apparatus; HLC-80/A manufactured by Toyo Soda Industry Co., Ltd., PA1 Column; Two TSK Gel-GMH columns or TSK Gel (G 3000 H+G 2000 H) columns, PA1 Eluent; Tetrahydrofuran PA1 Flow rate; 1 ml/min.
The calculated shrinkages in volume under discussion are given by the equation: ##EQU1##
With such known monomers that will polymerize with an appreciable shrinkage in volume, there are problems that they provide no dimensional accuracy when used as molding materials, and that where used as casting materials, they impose strains due to the shrinkage on castings and cause reduction in adhesion to a mold as well as inaccuracy of the dimension of the castings. There are further problems in use that such monomers may lead to reduction in cohesion to a substrate or formation of warpage due to the internal strains when used as paints or adhesives.
Therefore, for a number of industrial applications including precision castings, strain-free composites, paints and adhesives, it is highly desirable to have monomers which will present nearly zero shrinkage or positive expansion in volume on polymerization.
Certain bicyclic monomers which may polymerize with expansion in volume have been reported by William J. Bailey as described in the afore-mentioned literature (J. Macromol. Sci. Chem.). According to the literature, the spiro orthocarbonate of the formula: ##STR1## indicates a positive expansion of 2 to 17% upon its ring-opening polymerization.
We have closely studied in search of cyclic compounds which have not been described in literature and which will polymerize with no substantial change or appreciable expansion in volume. As a result, we have now discovered new bicyclic orthoester compounds which do, in most cases, indicate a considerable expansion during the ring-opening polymerization and which may be prepared from commercially available compounds in a facile way.
An object of this invention is to provide new bicyclic orthoester compounds which can undergo cationic ring-opening polymerization without substantial shrinkage or with positive expansion in volume. Another object of the invention is to provide processes for the preparation of these bicyclic compounds.
Further object of the invention is to provide polymers derived from the bicyclic compounds, the polymers having a specific gravity of substantially equal to or lower than that of the monomer compounds from which the polymers have been derived.
Other objects and advantages of this invention will become apparent from the following descriptions.